1. Field of the Invention
The present invention is directed to an apparatus and process for detecting the instantaneous load and/or continuous load on a transporting means, and in particular on a lifting mechanism, comprising a load measuring device and an electric motor as a driving means for lifting and lowering the load.
2. Description of Related Art
Load measuring devices for hoists are known. German patent publication 28 23 401 A1 discloses a load measuring device for a hoist with a lifting mechanism motor arranged in the load carrying means and which detects the load using a tension measurement rod. The tension measurement rod includes a wire strain gauge, the electrical resistance of which changes or varies as a function of the carried load imposed on the lifting mechanism whereby an electrical signal proportional to the carried load is generated by detecting the resistance of the wire strain gauge or the voltage drop across the gauge at a constant current flow. A special bridge circuit of the wire strain gauge and resistors is used to precisely determine the carried load. This load measuring device may be employed to continuously monitor the load of the lifting mechanism and protect against overloading thereof by connecting the device to electronic warning devices which automatically switch off the lifting mechanism when a nominal load is exceeded. The measuring elements of this conventional load measuring device are arranged in specially constructed carrying parts of the lifting mechanism or crane, an arrangement that increases the overall cost of the device. Moreover, the conversion steps or operations necessary to retrofit existing operating lifting mechanisms with this load measuring device are relatively expensive and time-consuming.
Load measuring devices are also used to detect load characteristics of lifting mechanisms by determining and summing destructive load values with the aid of the measured carried loads while taking the loading duration into account. In this regard, German patent publication 2 95 03 416 U1 discloses a device for determining the dynamic stress of structural component parts, plants and machinery; the device measures load values over several load changes and stores the summed value in a memory in order to monitor plant stress. A warning signal is triggered when the summed total load value is exceeded. Existing lifting mechanism devices already in operation may be refurbished and/or replaced with this type of load measuring device in a relatively short conversion process and in accordance with relevant legal regulations and guidelines so as to optimize the service life of the lifting mechanism. This process and system, however, disadvantageously incurs a relatively high cost of operation to detect the total load and in monitoring the useful life threshold.
A known method for determining the summed load values of a lifting mechanism is to connect an operating time meter to the device, as for example in the power supply feed to the lifting motor. This relatively simple method, however, only roughly measures the continuous load on the lifting mechanism. As a result, allowances must be made for the gross inaccuracy of this method of detecting total load by selecting appropriately high safety or error margins. As a result, lifting mechanisms that generally operate in the lower partial load range are typically prematurely i.e., before the device actually reaches its fullest inherently possible service life, refurbished or replaced for safety reasons and in order to meet applicable legal regulations and guidelines, thus resulting in increased costs.
The object of the present invention is therefore to provide a device for detecting the instantaneous load and/or continuous load on a lifting mechanism and requiring no modifications or additions to the mechanism's carrying parts or carrying gear while providing an accurate measurement. It is also an object of the invention to provide a relatively simple detection device for accurately determining the continuous load on a lifting mechanism.